COLUMBIA, S.C.  Children are supposed to play, run, jump and be active for at least two hours a day, but most aren't doing even half that much at preschool, says one of the first large studies to examine physical activity in children ages 3 to 5.

This low activity level could be contributing to the increasing problem of excess weight in kids, says researcher Russ Pate, a professor of exercise science at the University of South Carolina-Columbia.

About 10% of children ages 2 to 5 are overweight; another 12% are at risk of becoming so, the latest government statistics show. More than half of 3- to 5-year-olds go to preschool.

Children need more vigorous play during unstructured free time at preschool, Pate says, and they also need more organized physical activities, like dancing the hokey-pokey.

In the study, Pate and colleagues examined activity levels of 281 kids at nine preschools in Columbia, S.C., including church-based, private programs and Head Start.

The children wore accelerometers, a small activity monitor, for about 4 hours a day. Researchers also watched their activities. Among findings published in November's Pediatrics:

• The kids did an average of 7.7 minutes an hour of moderate to vigorous activity at preschool. Often it was done in blocks of time when the children were outside.

• Boys were more likely to participate in moderate or vigorous physical activity than girls. That has been consistent at all ages, Pate says. "What's interesting is we're observing that in kids this young."

• Children ages 4 to 5 were more likely to be sedentary and had fewer times of light activity, like walking slowly, than 3-year-olds. All movement, even light activity, matters when it comes to controlling weight, Pate says.

Pate was on a committee that 10 years ago advised that adults get at least 30 minutes of moderate activity most days of the week.

"If (kids) are not getting enough activity at school, then it's not likely they will get the remaining activity after they leave," he says. Still, "we encourage parents to make sure their children are active at home."

His best advice: Getting outside, "one of the most consistent and strong predictors of activity." That's true for kids of all ages, he says.

Others agree that activity is critical for preschool children.

"One of the trends we've seen is that the focus of many preschool programs may be becoming more narrow, focusing on cognitive development such as preliteracy, premath skills," says Mark Ginsberg of the National Association for the Education of Young Children, an organization of more than 100,000 early childhood professionals. "Our feeling is that programs also need to address social, emotional and physical development."